Electric furnace.



No. 792,022. PATENTED JUNE 13, 1905. E. HAAGN.

ELEGTRIC FURNACE.

APPLICATION FILED IAB. 8, 1905.

UNITED STATES Patented June 13, 1905.

PATENT OFFICE.

ERNST 'HAAGN, OF HANAU, GERMANY, ASSIGNOR TO THE FIRM OF C. HERAEUS, OFHANAU, GERMANY.

ELECTRIC FURNACE.

SPECIFICATION forming part of Letters Patent No. 792,022, dated June 13,1905.

Application filed March 8, 1905. Serial No. 248,970.

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Be it known that I, ERNST HAAGN, a subject of the German Emperor, and aresident of Hanan, (Jrermany, have invented certain new and usefulImprovements in Electric Furnaces, of which the following is aspecification.

My invention relates to a simple device for indicating the propercurrent strength at varying temperatures for electric furnaces, whichdevice may be arranged as an automatic cut-out to prevent the currentstrength from exceeding a certain limit.

1 will proceed to describe my invention, with re feren cc to theaccompanying d rawing, which represents a vertical cross-section throughan electric nm'fiie-furnace and shows the device.

The electric conductors leading to and from electric furnaces withheating resistances, such as mufiles or the like, are very liable tomelting the moment the furnace attains a high temperature. Evidently thetemperature of the conductor is determined, on the one hand, by theelectric energy conducted by it, and, on the other hand, by thetemperature of the surrounding parts of the furnace. The higher thetemperature of the furnace is of course the smaller is the currentstrength which the conductor will be able to withstand without melting.

For insuring a quick heating of the electric furnace usually a highstrength of the current is employed at the beginning, and afterward thiscurrent strength is gradually reduced as the temperature of the furnaceincreases. In order to effect this preliminary heating of the furnace ina safe manner, it was hitherto necessary to watch the ten'iperature ofthe furnace and to employ an ampere-meter.

The electric furnace l), illustrated in the drawing, is made of anysuitable material and. shown as placed on a convenient support Itcomprises a heating or melting chamber 0, into which a charge to beheated or melted (as the case may be) can be introduced in any knownmanner. Two binding-posts 7t and are shown as disposed beneath thefurnacet and connected with the two conductors v, and Z, whose endsterminate in the heating or melting chamber 0, as usual. A recess (Z isprovided in the wall of the furnace I) and made to extend to near 5 maybe a wire or a strip of sheet metal of the required strength and can beeasily watched from without. The two binding-posts g and 71. areconnected by the two conductors m. and a with the respective source ofelectricity.

The simple device t. 6., the wire or strip 0 5 is connected in serieswith the heating resistance.

The device operates as follows: On sending the current of a certainstrength through the circuit the furnace will be gradually heated, 7

so that the wire or strip a is not only heated by the electric current,but also by the heat of the furnace I), so that it will soon become red.As it is made of a certain metal or alloy and the red heat can be easilyrecognized, it

is possible to know the temperature of the furnace and to determine theproper strength of the current. The latter should be so regulated byreducing it from time to time that the wire or strip a. maintains itscolor of a commencing red. Then the conductors '2' and Z; will be ableto conduct the current in a safe manner without melting no matter whattemperature the furnace b may have.

W here so preferred, the device (1 may be ar- 5 ranged as an automaticcut-out, as it is only necessary to make it of a metal (for example,silver) or an alloy the melting-point of which is a little above thetemperature at which it commences to become red. the device will serveas a safety means, it melting under an overcharge, the strength of thecurrent being in all cases the lower the higher the temperature of thefurnace is.

The simple device maybe varied without deviating from the spirit of myinvention.

This 55 Then 9 What I claim as my invention, and desire to secure byLetters Patent, is-

1. In an electric furnace, the combination With a recess in the Wall ofthe furnace and reaching to near its heating or melting chamber, of aconductor-piece leading to said heating or melting chamber and engagingin said recess near its end face, a conductor engaging in said recess,and a metal indicator connecting the ends of said conductor-piece andsaid conductor in said recess and being so disposed, that it can beWatched from Without and indicate by its commencing red heat the correctstrength of the current. r

2. In an electric furnace, the combination with a recess in the Wall ofthe furnace and reaching to near its heating or melting chamber, of aconductor-piece leading to said heating or melting chamber and beingbent Without, so that its other end engages in said recess and reachesto the end face of the latter, a conductor engaging in said recess, anda metal indicator connecting the ends of said conductor-piece and saidconductor in said recess and being so disposed, that it can be Watchedfrom Without and indicate by its commencing red heat the correctstrength of the current.

3. In an electric furnace, the combination With a recess in the Wall ofthe furnace and reaching to near its heating or melting chamber, of aconductor-piece leading to said heating or melting chamber and beingbent Without, so that its other end engages in said recess and reachesto the end face of the latter, a conductor engaging in said recess, anda metal rod connecting the ends of said conductor-piece and saidconductor in said recess and adapted to be Watched from Without, so thatit can indicate by its commencing red heat the correct strength of thecurrent.

4. In an electric furnace, the combination with a recess in the Wall ofthe furnace and reaching to near its heating or melting chamber, of aconductor-piece leading to said heating or melting chamber and beingbent without, so that its other end engages in said recess and reachesto the end face of the latter,

a conductor engaging in said recess, a metal rod connecting the ends ofsaid conductorpiece and said conductor in said recess and adapted to beWatched from Without, a second conductor leading to said heating ormelting chamber, a source of electricity connecting the other ends ofsaid two conductors, and means for regulating the strength of thecurrent, said metal rod indicating by its commencing red heat thecorrect strength of the current.

5. In an electric furnace, the combination With a recess in' the Wall ofthe furnace and reaching to near its heating or melting chamber, of aconductor-piece leading to said heating or melting chamber and beingbent Without, so that its other end engages in said recess and reachesto the end face of the latter, a conductor engaging in said recess, arod connecting the ends of said conductor-piece and said conductor insaid recess and adapted to be Watched from Without, a second conductorleading to said heating or melting chamber, a source of electricityconnecting the other ends of said two conductors, and means forregulating the strength of the current, said rod being made of a metalWhose melting-point is a little above the red heat and this rodindicating by its commencing red heat the correct strength of thecurrent.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing Witnesses.

ERNST HAAGN.

W'itnesses:

JEAN GRUND, CARL GRUND.

